(CNN) - Vice President Joe Biden was back on the campaign trail Saturday, stumping in Louisiana for Sen. Mary Landrieu.

Landrieu, a Democrat in red Louisiana, could face an uphill battle for a fourth term in 2014.Follow @politicalticker

The vice president heaped praise upon her in remarks that lasted about 20 minutes, according to a pooled account of the fundraiser.

"I have never, never, never seen anyone fight harder for her state," Biden said. "I have never seen anyone who's more effective for her state."

Three non-partisan political race watchers describe the campaign as close.

The Cook Political Report says it leans Democratic, Capitol Hill newspaper Roll Call assesses it as a toss-up between the parties, and the Rothenberg Political Report scores the race as "Toss-up/Tilt Democrat."

Landrieu is considered a conservative Democrat. Recently, she and the state's other senator, Republican David Vitter, called for President Barack Obama to sign off on the Keystone XL pipeline that stretches from Canada to the Gulf Coast region. The pipeline project has broad Republican support but is generally met with more skepticism from Democrats and environmental groups.

Biden described her as someone who "is not an absolutist, not an ideologue. ... She's consistently ranked as one of the most bipartisan members."

She "makes the case for Louisiana, and everybody knows that if they don't vote with her, she'll make their lives miserable," he said. "She can exasperate the hell out of everybody and make them feel better for it."

The Louisiana Republican Party used Biden's visit to stir the waters ahead of the 2014 midterm election. It first called on Landrieu to call off the event because of Biden's recent remarks on gun control, then urged Landrieu to confront Biden over forgiveness for Hurricane Katrina loans.

"Mary Landrieu is the 'Last Liberal Standing' in Louisiana, so now she has to bring in liberals from other states to help her campaign," party chairman Roger Villere said in a statement.

Ticket prices at the fundraiser ranged from $250 to $2,500. Approximately 450 people attended, according to the pool account. She was introduced by her brother, who is the mayor of New Orleans.

Her likely challengers include three Republicans: former U.S. Rep. Jeff Landry and U.S. Reps. Bill Cassidy and John Fleming.